U.S. patent application number 09/981786 was filed with the patent office on 2002-06-27 for electrophotographic carrier, developer using the same, and developing method.
This patent application is currently assigned to Dainippon Ink and Chemicals, Inc.. Invention is credited to Amaya, Shinji, Isonaka, Takeshi, Kogawara, Toshiro, Ohba, Katsunori.
Application Number | 20020081514 09/981786 |
Document ID | / |
Family ID | 18805504 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020081514 |
Kind Code |
A1 |
Ohba, Katsunori ; et
al. |
June 27, 2002 |
Electrophotographic carrier, developer using the same, and
developing method
Abstract
The present invention provides a carrier for electrophotography,
which is capable of charging the toner in the developer very
rapidly to a target electrostatic charge and at the same time, is
capable of maintaining the target electrostatic charge during
printing, so that the chemical fogging related to the slow charging
rate can be eliminated and the image density related to the
maintenance of the electrostatic charge can be preserved during
printing. The charging rate and the charge maintenance of the
electrophotographic carrier can be preserved if the carrier
composed of magnetic core particles and the resin coat satisfies
the following equation (B)>[(-19.4).times.(A)+31], wherein (A)
represents a carbon content (weight %) of the carrier and (B)
represents a ratio of the square root of the number of emitted
photoelectrons ((CPS).sup.1/2) and the photon energy (eV).
Inventors: |
Ohba, Katsunori; (Oyama-shi,
JP) ; Kogawara, Toshiro; (Iwatsuki-shi, JP) ;
Isonaka, Takeshi; (Ageo-shi, JP) ; Amaya, Shinji;
(Saitama-shi, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN & HATTORI, LLP
1725 K STREET, NW.
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
Dainippon Ink and Chemicals,
Inc.
Tokyo
JP
|
Family ID: |
18805504 |
Appl. No.: |
09/981786 |
Filed: |
October 19, 2001 |
Current U.S.
Class: |
430/111.32 ;
430/111.1; 430/111.4 |
Current CPC
Class: |
G03G 9/1131 20130101;
G03G 9/1085 20200801; G03G 9/1139 20130101; G03G 9/1136
20130101 |
Class at
Publication: |
430/111.32 ;
430/111.1; 430/111.4 |
International
Class: |
G03G 009/10; G03G
009/113 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 27, 2000 |
JP |
P2000-328679 |
Claims
What is claimed is:
1. An electrophotographic carrier obtained by coating magnetic
particles with a resin, wherein the carrier satisfies the following
equation (B)>(-19.4).times.(A)+31, wherein, (A) represents a
carbon content in weight percent, and (B) represents a ratio of a
square root ((CPS).sup.1/2) of the number of emitted photoelectrons
(CPS) to a excitation photon energy (eV).
2. A carrier according to claim 1, wherein magnetic particles as
the core material of the carrier is made of ferrite.
3. A carrier according to claim 1, wherein the resin which forms
coating of the magnetic particles is a silicone resin.
4. An electrophotographic developer, which is provided with a toner
comprising at least a colorant and a binder resin, and the carrier
according to claim 1.
5. An electrophotographic developer according to claim 4, wherein
said toner is made of polyester resin.
6. An electrophotographic developer used according to claim 4,
wherein said toner contains a charge control agent which has a
positively charging capability.
7. A method for developing electrostatic images using the
electrophotographic developer according to claims 4 to 6.
8. A method of developing electrostatic images using the
electrophotographic developer according to claims 4 to 6 at a
developing speed of more than 20 m/minute.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to magnetic carriers used for
charging toners contained in a two component-type
electrophotographic developer comprising the carrier and the toner,
the electrophotographic developers containing the same carrier, and
to a developing method.
[0003] 2. Description of the Related Art
[0004] One of the important properties required for a magnetic
carrier used as one component of an electrophotographic developer
is a quick charging property of a toner, which is another component
of the electrographic developer. The magnetic carrier is required
to charge the toner rapidly. In other words, the carrier is
required to have a high charge build-up rate. If a portion of the
toner supplied into the developing machine while printing does not
charge rapidly, this portion of the toner will have too low an
electrostatic charge for developing the image, and the toner may be
scattered on printed sheets including on the background portion. As
a result, the insufficiently charged toner will contaminate the
prints, causing a phenomenon called "photographic foggingging" or
"chemical foggingging". In order to eliminate the insufficient
charging and the photographic foggingging, various countermeasures
have been proposed conventionally. In particular, extensive studies
have been carried out in order to obtain superior magnetic core
materials in terms of properties of materials, particle size, the
surface coating, and further research was carried out to find
suitable resin materials and the effects of heat treatments on the
properties of the resin coated carriers. In order to reduce the
photographic fogging, several measures were conventionally proposed
such as improving the charging property of the carrier for the
toner and improving the electric resistance of the developer
composed of the carrier and the toner.
[0005] Examples of conventionally proposed techniques follow.
Japanese Patent Application, First Publication No. Sho 47-17435
proposes to employ a fluororesin. Japanese Patent Application,
First Publication No. Sho 60-19156 discloses that coating of a
silane-coupling agent makes it possible to improve image density to
a satisfactory level and to decrease the photographic fogging of
images. Japanese Patent Application, First Publication No. Sho
61-20464 proposes to incorporate a conductive material in a
silicone resin.
[0006] Japanese Patent Application, First Publication No. Sho
64-91144 discloses that a preferable image quality having no
photographic fogging, no uneven density, and no blurring can be
obtained by application of a mechanochemical treatment to silicone
resin coated carrier particles, wherein the mechanochemical
treatment is carried out by stirring the coated carrier particles
mechanically until the carrier particles can charge the toner
approximately 1.2 to 2.5 times. Japanese Examined Patent
Application, Second Publication No. Hei 6-73030 discloses that
carrier particles coated with a coating layer formed by a
fluororesin, in which fluororesin particles are dispersed, shows a
high image quality having no photographic fogging and a high
stability over time in maintaining the charge. Japanese Patent
Application, First Publication No. Hei 11-125934 discloses that a
sufficient amount of charge can be obtained for the toner from the
beginning of the printing by applying an impact force on the
carrier particles coated with a silicone resin so as to accumulate
a 1.5 times larger amount of electrostatic charge in the developer,
which results in obtaining a high quality image having no
photographic fogging over a long term.
[0007] However, photographic fogging is a complicated phenomenon
and a complete solution to this problem is not yet obtained. The
carrier is required to have characteristics such that the carrier
not only charges the toner quickly to a predetermined level, but
also the predetermined level of electrostatic charge must be
maintained constant while printing. This is because the image
density must be maintained constant while printing. A technique
compatible with the quick charging and the long-term charge
maintenance property is still a problem to be solved, because the
quick charging is related to preventing the photographic fogging
and the long-term charge maintenance property is related to the
time-dependent reliability of the image density.
[0008] Recently, the charging or electrification mechanism between
the carrier and the toner has been extensively studied. It is
assumed that one possible mechanism is that the toner is charged as
a result of an electron exchange process between the toner and the
carrier due to the difference of surface energy levels of the toner
and the carrier when the carrier is in contact with the toner. The
surface energy level is related to a property which is called a
work function. In general, when two substances having different
work functions are in contact, the substance having a lower work
function has a tendency to donate electrons (i.e., is likely to be
positively electrified).
[0009] Various methods are proposed for measuring the work function
of a substance, and, in general, the work function is obtained by
measuring photoelectrons emitted from an object when light beams of
various wavelengths are irradiated onto the object. Since the
photoelectrons will not be emitted if the irradiated light does not
exceed a certain energy level, an observation of the relationship
between the light wavelength (photon energy) and the photoelectron
emission makes it possible to obtain the minimum energy at which
the photoelectron emission starts. Not only light beams but also
X-rays or electron beams may be employed as the radiation, and the
measurement is performed in a vacuum chamber in order to carry out
an accurate observation of photoelectron emission.
[0010] Recently, however, a low energy electron counting apparatus
has been developed which carries out the measurement of the work
function by irradiation of ultraviolet light on an object in air.
The above-described apparatus is becoming widely used in the fields
of developers including toners and carriers for measuring their
work functions. Japanese Patent Application, First Publication
No.9-10610 defines the relationship between work functions of the
toner and the carrier. Japanese Patent (Granted) Publication No.
2954786 discloses that a toner having superior color
reproducibility can be obtained by identifying the differences of
work functions of three primary color toners.
[0011] However, merely the work function is not sufficient for
clarifying the electrostatic charging behaviors of the carrier and
the toner, although the work function is one of the measures with
respect to the charging performance. In the conventional carriers
and toners developed employing the work function as a measure of
electrification behaviors, a superior carrier is not yet available,
which has performances of both quick charging and the charge
maintenance properties, both of which are respectively required for
eliminating the photographic fogging of an image and for
maintaining the image density.
SUMMARY OF THE INVENTION
[0012] An object of the present invention is to provide a method of
developing electrostatic images by using a carrier for
electrophotography, which is compatible not only for the quickly
charging the toner but also for maintaining the necessary charge
during printing.
[0013] The first aspect of the present invention provides an
electrophotographic carrier by coating magnetic particles with a
resin, wherein the carrier satisfies the following equation
(B)>(-19.4).times.(A)+31, wherein, (A) represents the carbon
content in weight percent, and (B) represents the ratio of a square
root ((CPS).sup.1/2) of a number of emitted photoelectrons (CPS) to
a excitation energy (eV).
[0014] The second aspect of the present invention is related to an
electrophotographic developer, provided with a toner comprising at
least a colorant and a binder resin and the above-described
carrier.
[0015] The third aspect of the present invention provide a method
for developing electrostatic images using the above described
developer for the electrophotography.
[0016] According to the present invention, the use of the
electrophotographic carrier that satisfies the above-described
equation makes it possible to improve the charge build-up of the
toner and to reduce the time until the toner is charged to a
necessary amount of electrostatic charge. As a result, the chemical
fogging can be eliminated and the image density can be maintained
constant.
[0017] The inventors of the present invention prepared a number of
binary developers composed of various carriers and toners and the
charging and printing behaviors of toners were evaluated in order
to examine the correlations between (A) corresponding to the carbon
content (weight %) of the carrier, and (B) which is a ratio of the
square root of the number of emitted photoelectrons ((CPS).sup.1/2)
and a excitation energy (eV). In test production of carriers, the
type and the amount of resin for coating the core particles of the
carrier were changed, and the shearing force applied to the carrier
during production and the method of surface coating were changed.
The relationship between (A) and (B) are shown in FIG. 3, by
plotting (A) on the horizontal axis for (A) and plotting (B) on the
vertical axis. The carriers which exhibit superior charging and
printing behaviors are marked by .smallcircle., carriers which
exhibit relatively good charging and printing behaviors are marked
by .sunburst., and carriers showing inferior charging and printing
behaviors are marked by .times.. The inventors of the present
invention discovered the fact that, as shown in FIG. 3, the
carriers which have a superior charging and printing behavior have
the value of (B) above the line expressed by
(B)=[(-19.4).times.(A)+31], that is, the value of (B) which is
greater than the value obtaining by calculating the formula
[(-19.4).times.(A)+31].
[0018] The value of (A) is a carbon content of the carrier obtained
by calculating from the amount of carbon dioxide and carbon
monoxide generated by firing the carrier in oxygen flow.
[0019] Specifically, (A) is a value obtained by dividing the total
carbon content obtained by measurement of amounts of carbon dioxide
and carbon monoxide generated at the time of combustion of the
resin coated carrier by the total weight of the carrier before
combustion. Accordingly, the value (A) of the present invention
means the carbon content (weight %) of the resin coated
carrier.
[0020] The carbon content is obtained by the following
conditions.
[0021] Sample weight: 0.5 g
[0022] Combustion temperature: 1250.degree. C.
[0023] Measuring time: 30 seconds
[0024] Measuring temperature: 25.degree. C.
[0025] Measuring humidity: 60%
[0026] The value (B) is obtained by the following conditions.
[0027] Test apparatus: AC-1 (Riken Keiki Co.)
[0028] Quantity of light: 500 nW
[0029] Anode voltage: 3300 to 3450 V
[0030] Distance between an object and a detector: 1 mm
[0031] Measuring range: 6.0 to 3.8 eV
[0032] Measuring time: 10 seconds /1 point
[0033] Measuring temperature: 25.degree. C.
[0034] Measuring humudity: 60%
[0035] Furthermore, explanations are provided below about the low
energy electron spectroscopic apparatus and the value (B) obtained
by the measuring values of the above apparatus. The low energy
electron spectroscopic apparatus AC-1 produced by Riken Keiki Co.
was used to measure the value (B) employed in the present
invention. FIG. 1 shows a schematic constitution of AC-1. A 500 nW
light source was used as the light source for the ultraviolet
light. The light beam emitted from the light source is separated
into optional beams having a wavelength in a range of 200 to 360 nm
and the separated lights are used for irradiation of the sample
surface. The light beams having a wavelength in a range of 200 to
360 nm have a light energy ranging from 6.0 to 3.4 eV. In the
present invention, the monochromatic beam having an energy range
from 6.0 to 3.8 eV is used as the light beam for irradiation in the
present invention. When an object is swept by the monochromatic
light beams in sequence from the lower energy beam to the higher
energy beam, the detector starts detecting a photoelectron emission
due to the photoelectric effect. The energy of the light beam at
which the photoelectron emission starts is the value called a
photoelectric work function (work function). Electrons emitted from
the sample ionize oxygen molecules in air and the ionized oxygen
molecules are transferred to the low energy electronic counter
(detector), where the ionized oxygen molecules emit electrons, and
the number of emitted electrons are counted. As a result, a linear
relationship is obtained between the square root ((CPS).sup.1/2) of
the number of emitted electrons and the excitation energy (eV). The
slope B in FIG. 2 is the value (B) of the present invention. That
is, the slope B [(CPS).sup.1/2/eV] is a ratio of the square root of
the number of emitted electrons (CPS).sup.1/2 and the excitation
energy (eV) and this slope B corresponds to the value (B) in the
equation of the present invention.
[0036] Note that the number of emitted electrons is measured in CPS
(Counts Per Second), which is the number of photoelectrons emitted
from the sample surface per second. The excitation energy (eV) is
the energy which is received by the sample.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a schematic diagram showing the structure of the
low energy electron spectroscopy apparatus.
[0038] FIG. 2 is a diagram showing the relationship between the
square root of the emitted number of photoelectron ((CPS).sup.1/2)
and excitation energy (eV) and the slope B
((CPS).sup.1/2/(eV)).
[0039] FIG. 3 is a diagram showing the relative relationship
between the factor A, which is the weight percent of carbon
contained in the carrier and the slope B, which is a ratio between
the root square of the emitted number of photoelectron
((CPS).sup.1/2) and excitation energy (eV).
DETAILED DESCRIPTION OF THE INVENTION
[0040] The carrier used for electrophotography employed in the
present invention is a carrier formed by coating magnetic particles
with a resin. Examples of the magnetic particles as the core
material of the carrier particles include powders of iron oxide,
magnetite, and ferrite. Ferrite is preferable as the carrier
powder, and the ferrite powder containing manganese is more
preferable because its properties, such as the charging property
and the electrical resistance, are preferably balanced.
[0041] Core particles in any shape such as a scale-shape or an
egg-shape can be used from the points of view of balancing
properties such as flowability, electrical resistance, and
electrification. Above all, spherical particles are most preferable
for the core material of the carrier because of its high
flowability. The core particles having an average particle size
ranging from 1 to 500 .mu.m can be employed. However, it is
preferable to employ core particles having average particle
diameters from 30 to 110 .mu.m.
[0042] Examples of resins used for coating the core particles
include polyethylene, polypropylene, polystyrene,
polyacrylonitrile, polyvinylacetate, polyvinyl alcohol,
polyvinylbutyral, polyvinylchloride, polyvinylcarbazol,
polyvinyletherpolyvinylketone, a vinlychloride/vinylacetate
copolymer, a styrene/acryl copolymer, straight silicone resin and
its derivatives constituted by an organosiloxane bond, fluororesin,
(meth)acrylate, polyester, polyurethane, polycarbonate, phenol
resins, amino resins, melamine resins, benzoquanamine, urea resins,
amide resins, epoxy resins, acrylpolyol resins.
[0043] In the above-described examples, silicone resins,
fluororesins, and (meth)acrylate resins are preferable because they
can provide coated particles having a stable charging property and
a high coat strength. As described above, a preferable carrier is
obtained by using ferrite as a core material and by coating the
core particles with more than one type of resin selected from the
group containing a silicone resin, fluororesin, and a
(meth)acrylate resin. In these resins, the silicone resin is
particularly preferable because toner is difficult to adhere on the
surface of the carrier particles. In addition, it is also possible
to carry out a crosslinking reaction of the coated resin after
coating for adjusting the strength of the coated resin and the
amount of charge. If necessary, it is possible to coat the carrier
particles by a resin homogeneously to a uniform thickness or to
coat to form dots so as to expose a part of the core surface.
[0044] In the coating resin, a conductivity regulator (such as
carbon black), a quaternary ammonium salt, and a catalyst may be
incorporated. Examples of the conductivity regulators include
carbon blacks such as acetylene black, channel black, furnace
black, and Ketchen black; metal carbide such as SiC and TiC; metal
nitride such as BN, NbN, and TiN; metal boride such as MoB, CrB,
and TiB.sub.2; metal oxide such as ZnO, TiO.sub.2, and SnO.sub.2;
and fine metal powders such as Al and Ni. The average particle
sizes represented as the number average diameter of these
conductivity regulators preferably lies within a ranges of 0.01 to
5 .mu.m, and more preferably within a range of 0.05 to 3 .mu.m.
This average particle size can be measured under a transmission
electron microscope. Above all, the most preferable conductivity
regulator is carbon black.
[0045] A method of forming the resin coated carrier will be
described below.
[0046] (1) A method of forming coated carrier particles by coating
a resin on the core carrier particles.
[0047] Although any method can be used to coat the resin film on
the surface of core particles, examples of coating methods include
a dipping method to coat the core particles by dipping into a resin
solution, a spray method by spraying the resin solution on the
surface of the core particles, a floating bed method by coating
while the core particles are floated by floating air, and a kneader
coater method by mixing the core particles with the resin solution
and removing a solvent thereafter. Although the solvents to be used
for the resin solution are not limited, examples of the solvents
include toluene, xylene, acetone, methylethylketone,
tetrahydrofuran, and dioxane. A problem arises in this case in that
the core particles will be adhered to each other by the coated
resin layer.
[0048] (2) In the case that a thermal crosslinking type resin (for
example, a silicone resin) is used, a thermal treatment is
conducted after coating at a temperature in a range of 150 to
300.degree. C. This thermal treatment thereby enhances crosslinking
of the coated resin but still a problem remains in that the carrier
particles adhere to each other.
[0049] (3) The coated carrier particles, which are adhered to each
other, are loosened and separated.
[0050] As described above, the coated core particles are produced
by the above methods. However, the core particles (magnetic
material) after coating are liable to aggregate. In order to loosen
the aggregated particles, the following loosening treatments are
adopted. A representative loosening process is conducted as
follows. The aggregated carrier particles are put into a sealing
container, if necessary, together with hard beads such as zirconia
beads and they are mixed and stirred. Stirring is industrially
conducted using mixers such as Henschel-type mixer, Nautor-type
mixer, and W-cone type blender for loosing the aggregate by
applying a shearing force and a carrier particles having a
predetermined particle size distribution are obtained.
[0051] The coated carrier particles are produced by, for example,
the above-described methods. In order to satisfy the relationship
between (A) and (B), it is preferable to treat the carrier
particles during the resin coating process or after the resin
coating process as follows.
[0052] (1) Adjustment of the shearing force applied to the
aggregate during loosening of the aggregate. The shearing force
applied to the aggregate can be adjusted by selecting the suitable
process conditions such as time, speed, and force for the loosening
process and by selecting a suitable loosening method. In general,
the value of (B) increases as the shearing force increases.
[0053] (2) The value of (B) can be increased by performing a dry
etching process to the carrier particles using an ion sputtering
apparatus, for example, after the normal loosening process.
[0054] When the amount of coated resin is increased, the right side
of the equation expressing the relationship between (A) and (B)
becomes small. However, the increasing amount of resin generally
decreases the value of (B), so that it is not preferable to
increase the amount of coated resin beyond what is necessary. The
necessary amount of the coated resin reduced as a carbon content is
preferably within a range of 0.05 to 3. 0%, more preferably within
a range of 0.1 to 1 .5%, and most preferably within a range of 0.3
to 0.9%.
[0055] The toner used in the present invention is not limited. Any
resin may be used for binding the toner without any limitation if
the resin can be ordinarily used for binding resin. Examples of
resins for binding toners include polystyrene,
styrene-(meth)acrylate ester copolymer resin, olefin resin,
polyester resin, amide resin, polycarbonate resin, epoxy-type
resins, and graft polymers of these resins and their mixtures.
[0056] Among these resins, in view of the charge stability, the
charge maintenance stability, fixing characteristics, and color
reproducibility when the resin is used for binding color toners
containing organic color pigments, it is preferable to use resins
including polyester resins, styrene-(metha)acrylate ester copolymer
resins.
[0057] The polyester resin used as a binder resin for the toner
used in the present invention is obtained, for example, by normal
dehydration condensation of dicarboxylic acid and diol. Examples of
dicarboxylic acid include dicarboxylic acids or their derivatives
such as phthalic anhydride, terephthalic acid, isophthalic acid,
orthophthalic acid, adipic acid, maleic acid, maleic anhydride,
fumaric acid, itaconic acid, citraconic acid, hexahydrophthalic
anhydride, cyclohexanedicarboxylic acid, succinic acid, malonic
acid, glutaric acid, azelaic acid, and sebacic acid.
[0058] Examples of diols include ethylene glycol, diethylene
glycol, propylene glycol, dipropylene glycol, tripropylene glycol,
butanediol, pentanediol, hexanediol, bisphenol A,
polyoxyethylene-(2,0)-2,2-bis(4-hyd- roxylphenyl)propane and its
derivatives, polyoxypropylene-(2,0)-2,2-bis(4--
hydroxylphenyl)propane,
polyoxypropylene-(2,2)-polyoxyethylene-(2,0)-2,2
bis(4-hydroxylphenyl)propane,
polyoxypropylene-(6)-2,2-bis(4-hydroxylphen- yl)propane,
polyoxypropylene-(2,2)-2,2-bis(4-hydroxylphenyl)propane,
polyoxypropylene-(2,4)-2,2-bis(4-hydroxylphenyl)propane, and
polyoxypropylene-(3,3)-2,2-bis(4-hydroxylphenyl)propane and its
derivative.
[0059] Examples of diols further include diols such as polyethylene
glycol, polypropylene glycol, ethylene oxide-propylene oxide block
copolymer diol, ethylene oxide -tetrahydrofuran copolymer diol, and
polycaprolactone diol.
[0060] Furthermore, if necessary, it is possible to use the
following compounds in combination with the above compounds, which
include more than trifunctional aromatic carboxylic acids and its
derivatives such as trimellitic acid, trillitic anhydride,
pyromellitic acid, and pyromellitic anhydride; trifuctional
alcohols such as sorbitol, 1,2,3,6-hexanetetraol, 1,4-sorbitane,
pentaerythritol, 1,2,4-butanetriol, 1,2,5-pentaerythritol,
glycerine, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol,
trimethylolethane, trimethylolpropane, 1,3,5-trimethylolbenzene;
more than trifunctional polyhydric epoxy compounds such as
bisphenol A-type epoxy resin, bisphenol F-type epoxy resin,
ethyleneglycoldiglycyldiether, hydroquinondiglycidyldiether, N,
N-diglycidylaniline, glycerinetriglycidylether,
trimethylolpropanetriglyc- idylether,
trimethylolethanetriglycidylether, pentaerythritoltetraglycidyl-
ether, cresolnovolak-type epoxyresin, phenolnovolak-type
epoxyresin, polymers or copolymers of vinyl compounds having epoxy
groups, epoxidated resorcinol-acetone condensation products,
partially epoxidated polybutadiene, and more than one type of
semi-drying or drying fatty-acid ester epoxy compounds.
[0061] The above-described polyester resins are obtained by
dehydration condensation reactions or the ester exchange reactions
using the above-described material components. Although the
reaction time and the reaction temperature of the above reactions
are not limited, it is preferable to carry out these reactions at
temperatures ranging from 150 to 300.degree. C. for 2 to 24
hours.
[0062] The above-described reactions are conducted in the presence
of suitable catalysts such as zinc oxide, stannous oxide,
dibutyltuin oxide, and dibutyltindiuranate.
[0063] Any type of polyester resin may be used as the binder of the
toner if the resins have suitable glass transition temperature and
suitable viscosity characteristics when melted. From the point of
view of the fixing property, a characteristic temperature of the
polyester resins, at which the viscosity reaches 1.times.10.sup.5
poise, is preferably equal to or higher than 95.degree. C., and
more preferably, the characteristic temperatures range from 95 to
170.degree. C., and most preferably, the characteristic
temperatures range from 95 to 160.degree. C.
[0064] On the other hand, the glass transition temperature (Tg) of
the polyester resins is preferably equal to or higher than
40.degree. C. The acid value of the polyester resins is preferably
lower than 30. If the acid value is too high, a necessary amount of
charge may not be obtained, since the resin will prevent the
electrification of the toner.
[0065] Examples of styrene monomers used for resins obtained by
copolymerization of styrene-(meth)acrylateester include styrene,
.alpha.-methylstyrene,vinyltoluene, p-sulfonstyrene,
dimethylaminomethylstyrene.
[0066] Examples of (meth)acrylate ester monomers include
alkyl-(meth)acrylates such as methyl (meth)acrylate, ethyl
(meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate,
n-butyl (meth)acrylate, isobutyl (meth)acrylate,
tertiary-butyl(meth)acry- late, octyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, lauryl (meth)acrylate, and stearyl
(meth)acrylate; alicyclic (meth)acrylates such as cyclohexyl
(meth)acrylate; aromatic (meth)acrylates such as benzyl
(meth)acrylate; hydroxyl group containing (meth)acrylates such as
hydroxyethyl (meth)acrylate; phosphate group containing
(meth)acrylates such as (meth)acryloxyethylphospahte; halogen atom
containing (meth)acrylates such as 2-chloroethyl (meth)acrylate,
2-hydroxy-3-chloropropyl (meth)acrylate, and 2, 3-dibromopropyl
(meth)acrylate; epoxy-group containing (meth)acrylates such as
glycidyl (meth)acrylate; ether-group containing (meth)acrylates
such as 2-methoxyethyl (meth)acrylate and
2-ethoxyethyl(meth)acrylate; basic nitrogen atom or amide-group
containing (meth)acrylates such as dimethylaminoethyl
(meth)acrylate and diethylaminoethyl (meth)acrylate.
[0067] In addition, if necessary, it is possible to use
copolymerizable unsaturated compounds in combinations with these
compounds shown above in the copolymerization reactions of
styrene-(meth)acrylate ester. Examples of copolymerzable
unsaturated compounds include carboxyl-group containing vinyl
monomers such as (meth)acrylate, itaconic acid, crotonic acid,
maleic acid, and fumaric acid; sulfoggingroup containing vinyl
monomer such as sulfoethylacrylamide; nitryl-group containing vinyl
monomer such as (meth)acrylonitryl; ketone-group containing vinyl
monomers such as vinylmethylketone and vinylisopropenylketone;
basic nitrogen atom or amide-group containing vinyl monomers such
as N-vinylimidazol, 1-vinylpyrrol, 2-vinylquinoline,
4-vinylpyridine, N-vinyl-2-pyrrolidone, and N-vinylpiperidone.
[0068] Furthermore, a crosslinking agent may be used in the
copolymerization reaction within a range of 0.1 to 2 weight %.
Examples of crosslinking agents include divinylbenzene,
divinylnaphthalene, divinylether, ethyleneglycol di(meth)acrylate,
diethyleneglycol di(meth)acrylate, triethyleneglycol
di(meth)acrylate, polyethyleneglycol di(meth)acrylate,
1,3-butyleneglycol di(meth)acrylate, 1,6-hexaneglycol
di(meth)acrylate, neopentylglycol di(meth)acrylate, propyleneglycol
di(meth)acrylate, dipropyleneglycol di(meth)acrylate,
polypropyleneglycol di(meth)acrylate, trimethylolpropane
tri(meth)acrylate, tetramethylolmethane tetra(metha)acrylate.
[0069] In contrast, styrene-(meth)acrylate resins obtained by
copolymerization of the above-described carboxyl-group containing
vinyl monomers may be further crosslinked by use of halides,
hydroxides, oxides, carboxylic acids, alkoxylates, and chelates of
metal salts containing Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn,
Ni, Pb, Sn, Sr, and Zn, etc. The crosslinking reaction can be
conducted in the presence of solvents by heating and stirring.
[0070] Copolymerization of styrene-(meth)acrylate ester may be
implemented by use of various polymerization methods such as
solution polymerization, dispersion polymerization, and block
polymerization in the presence of a polymerization catalyst.
[0071] Examples of the polymerization catalysts include 2,2'-azobis
(2,4-dimethylvaleronitril), 2,2'-azobisisobutylonitril,
1,1'-azobis(cyclohexane-1-barbonitril), benzoylperoxide,
dibutylperoxide, and butylperoxidebenzoate. The amount of the
catalyst used in the polymerization reaction is preferably in a
range of 0.1 to 10 weight % of the vinyl monomer.
[0072] The above-described styrene-(meth)acrylate ester copolymers
my be used for the two-component development toner, if the
copolymers have an appropriate glass transition temperature and an
appropriate characteristic temperature obtained from the
melt-viscosity characteristics. The characteristic temperature, at
which the viscosity of the melt reaches 1.times.10.sup.5 poise, is
preferably higher than 95.degree. C., is more preferably in a range
of 95 to 170.degree. C. from the point of view of fixing property
at lower temperatures, and is most preferable when the
characteristic temperature is in a range of 95 to 160.degree.
C.
[0073] The glass transition temperature (Tg) of the above-described
styrene-(meth)acrylate copolymers is preferably equal to or more
than 40.degree. C., and a more preferable range is 45 to 85.degree.
C.
[0074] In addition, the acid value of the copolymer is preferably
below 30, and more preferably below 15. If the acid value is too
high, the amount of charge of the toner is reduced because such
copolymers degrade the charging property of the toner.
[0075] The toner used for preparing the developer in combination
with the electrophotographic carrier of the present invention is
not limited to any one of negatively charged or positively charged
toners. The positively charged toner containing the polyester resin
is preferably used in combination with the styrene-acrylate type
toner, since the toner using the styrene-acrylate type polymer has
problems because the toner is hard to charge positively and the
positive charge is not stably maintained during printing.
[0076] When a low melting polyester resin having a linear chain
structure is used in combination with the high melting polyester
resin having a branched or crosslinked structure, a preferable
toner is obtained which exhibit prominent low temperature fixing
properties and excellent offset-preventing properties. The branched
and crosslinked polyester resin is produced by use of polyhydric
alcohol containing more than three hydroxide groups.
[0077] Various colorants such as carbon black, various organic
pigments, inorganic pigments, dye may be used for the toner of the
present invention without any limitation. Examples of colorants
follow.
[0078] The following known colorants are used in the toner.
Examples of black colorants include carbon blacks such as furnace
black, channel black, acetylene black, thermal black, lamp black,
and Ketchen black, which are named by production methods. Examples
of blue colorants include C. I. Pigment Blue 15-3 in a
phthalocyanine system and C. I. Pigment Blue 60 in an
indanthrone-system; red colorants include C. I. Pigment Red 122 in
a quinacridone-system, C. I. Pigment Red 48:1 C. I. Pigment Red
43:3, and C. I. Pigment Red 57:1 in an azo-system; yellow colorants
include C. I. Pigment Yellow 12, C. I. Pigment Yellow 13, C. I.
Pigment Yellow 14, C. I. Pigment Yellow 17, C. I. Pigment Yellow
97, and C. I. Pigment Yellow 155, in the azo system, C. I. Pigment
Yellow 110 in an isoindolinone system, C. I. Pigment Yellow 151, C.
I. Pigment Yellow 154, C. I. Pigment Yellow 180, and C. I. Pigment
Yellow 185 in a benzimidazolon system. It is preferable to
incorporate the colorant within a range of 1 to 20 weight parts.
These colorants may be used in combination of two or more.
[0079] Although the ratio of the resin and colorant is not limited,
the preferable ratio of the colorant to the resin is within a range
of 1 to 30 weight parts, and more preferably within a range of 1 to
10 weight parts.
[0080] When color toners are produced by use of these colorants, it
is preferable to use polyester resin from the point of view of
superior coloring and transparency in printing. Polyester resin is
suitable for the color toner resin because of its superior
toughness to be able to tolerate the stress during printing and its
low melting point.
[0081] Although the toner of the present invention is not limited
to a positively charged toner or a negative charged toner, various
charge control agents may be used depending on need. Examples of
positive charge control agents include triphenylmethane-system
dyes, nigrosine-system dyes, quaternary ammonium salt compounds, or
resins containing an amino group, and a particularly preferable
agent is a combination of a nigrosine-system dye and a quaternary
ammonium salt. Preferable examples of the quaternary ammonium salt
compounds include Bontron P-151 (a trade name of a product of
Orient Chemical Co.), TP-302, TP-415, and TP-610 (trade names of
products of Hodogaya Kagaku Co.).
[0082] When a combination of a nigrosine -system dye and a
quaternary ammonium salt compound is used, a preferable ratio of
both compounds is in a range of 1/9 to 9/1, and more preferable
ratio ranges from 2/8 to 8/2. Although the nigrosine-system dyes
have a high charging capability, homogeneous and stable
electrification is often not obtained, so that the use of a single
nigrosine-system dye often causes photographic fogging and the
resultant printed image insufficiently sharp. In contrast, although
the quaternary ammonium salt compounds exhibits homogeneous and
stable charging, the capability for positive charging is low, so
that it is desirable to use the quaternary ammonium salt compounds
in combination with the nigrosine-system dye for obtaining a sharp
printed images without fogging during continuous printing. When the
content of the nigrosine-system dye is lower than 10%, the toner
will not be sufficiently charged and the transfer efficiency of the
toner to the paper is degraded. As a result, the image quality of
prints, especially background portions of the prints are degraded
and the image resolution is also degraded. The scattering of the
toner increases as a result of low electrification of the toner.
When the content of the nigrosine-system dye is higher than 90%,
the toner will be excessively charged so that this toner produces
low density and low quality images containing dense fogging.
[0083] The proper electrification is not obtained if both compounds
are not mixed in a proper ratio, and the toner having improper
electrification will produces prints with low quality and low
resolution having dense fogging. An optimum amount of
electrification will be obtained by properly adjusting the ratio of
both compounds, and a toner can be provided which is capable of
developing highly dense, high quality and clearly outlined prints
having no scattered toner.
[0084] Any negative charge control agent may be used without
limitation if the agent can impart a negative charge to the toner.
Preferable examples of the negative charge control agents include
azo-system complex (salts), salicylate-system metal complex
(salts), benzylic acid metal complex (salts), tetraphenyl complex
(salts), calixarene-type phenol-system condensation products,
cyclic polysaccharides, and resin-base charge control agents.
[0085] Examples of the azo-system complex salts include "BONTRON
S-34" and "BONTRON S-44" (above are trade names of products by
Orient Chemicals Co.)
[0086] Examples of the salicylate-system metal complex salts
include "BONTRON E-81 ", "BONTRON E-84", and "BONTRON E-88" (the
above are trade names of products by Hodogaya Kagaku Co.). Examples
of benzylic acid metal complex salts include "LR-147" and "LR-297"
(the above are tradenames of products by Japan Carlit Co.). An
example of tetraphenyl complex salt is "COPY CHARGE NX" (tradename
of a product of Clariant Co.). Exmples of the carixarene type
compounds include "BONTRON E-89" and "BONTRON F-21" (the above are
trade names of products by Orient Chemical Co.). An example of the
cyclic polysaccharides includes "COPY CHARGE NCA" (the above is a
tradename of a product by Clariant Co.).
[0087] Example of the resin-base charge control agents include
"FCA-1001-NS (a tradename of a product of Fujikura Kasei Co.) and
"COPY LEVEL NCS" (a tradename of a product by Clariant Co.).
[0088] The toner suitable for using the electrophotographic carrier
of the present invention is a positively charging toner, which uses
polyester resin as a binder resin. In addition, the toner is
preferably containing a positive charge control agent.
[0089] The content of the charge control agent is preferably in a
range of 0.3 to 10 weight parts per 100 eight parts of binder
resin, and more preferably in a range of 1 to 5 weight parts.
[0090] When this toner is fixed using a heat roll fixing method,
various waxes are incorporated in the toner, if necessary, for
releasing the toner from the heat roll as an auxiliary agent in
order to prevent problems caused by adhesion of the toner (offset).
Examples of waxes include natural waxes such as montanic acid ester
wax; and polyolefin-type waxes such as high pressure process
polyethylene and polypropylene.
[0091] Among various waxes, it is particularly preferable in the
present invention to employ carnauba wax, montanic ester wax, rice
wax and/or coccid wax, since these waxes exhibit prominent
dispersibility particularly in polyester resin and improve fixing
and offset-preventing performances.
[0092] It is preferable to use non free fatty acid carnauba wax
after removing free fatty acid by refining. The non free fatty acid
carnabau wax preferably has an acid value of less than 8, and more
preferably, less than 5. The non free fatty acid carnabau wax can
be crystallized into finer crystals and has an improved
dispersibility in polyester resin. The montanic ester wax is
obtained by refining a mineral, and the refining process makes this
wax to be crystallized into finer crystals and the dispersibility
in polyester resin is improved, similarly to the case of the above
carnauba wax. The acid value of the montanic ester wax is
preferably less than 30.
[0093] In addition, the rice wax is obtained by refining a rice
bran wax and its acid value is preferably less than 13. The coccid
wax is obtained by collecting wax-like component secreted by larvae
of the scale insect after dissolving it in hot water, separating
the upper layer, and solidifying. The coccid wax obtained by the
above refining process is a white solid, which has a very sharp
meting point, and is suitable for use in the toner of the present
invention. The acid value of this coccid wax is preferably less
than 10, more preferably less than 5.
[0094] The above-described wax may be used alone or in combination.
A preferable fixing property and a offset-preventing property are
obtained by incorporating the wax in a range of 0.3 to 15 weight
parts of binder resin, preferably in a range of 1 to 5 weight
parts. If the content is lower than 0.3 weight parts, the
offset-preventing property is degraded, and if the content is
higher than 15 weight parts, the fluidity of the toner is degraded
such that a part of the toner adheres on the carrier surface and a
part of the carrier surface is immobilized, which deteriorates the
charging property of the toner by carrier particles.
[0095] In addition to the above-described natural waxes, synthetic
ester waxes may be preferably used. Examples of the synthetic ester
waxes include tetrabehenic acid esters of pentaerythritol. Note
that it is possible to jointly use other synthetic waxes such as
polypropylene wax and polyethylene wax.
[0096] The toner used in the present invention may be produced by
employing generally known manufacturing methods, and not by any
particular manufacturing process. A typical manufacturing method
for obtaining the toner includes mixing the resin and the colorant,
melting and kneading the mixture above the meting point (softening
point), cooling and pulverizing, and sieving.
[0097] More practically, the mixture composed of the essential
components of the resin and the colorant are mixed by a kneading
machines such as a two-roll kneder, a three-roll kneader, a press
kneader, and a two-axial extruder. The mixing is performed for
dispersing the colorant homogeneously in the resin medium. Although
kneading conditions are not particularly limited if the above
objective is attained, the kneading time ranges from 30 seconds to
2 hours at a normal kneading temperature of 80 to 180.degree. C. In
order to disperse the colorant in the resin, the colorant may be
mixed with the resin medium as a pretreated powder by a flashing
treatment or as a master batch which is prepared by melt kneading a
batch containing a high concentration of the colorant.
[0098] After the kneading operation, the kneaded product is
pulverized by, for example, a jet mill and sieved by, for example,
a blower classifier.
[0099] Although there is no particular limitation, the average
particle size of the toner matrix is normally adjusted in a range
of 5 to 15 .mu.m.
[0100] Additives are then externally added to the toner matrix and
mixed with the toner matrix by use of, for example, a Henschel-type
mixer.
[0101] The additives are used for improving the quality of the
toner surface, aiming to improve the fluidity of the toner or to
improve the electrification property. Examples of these additives
include inorganic fine powers such as silicon dioxide, titanium
oxide, and alumina, these powders after surface treatment to be,
for example, hydrophobic, and resin powders.
[0102] As examples of silicon oxide include hydrophobic silica
powder which is obtained by surface treatment of the silica powder
with a polyorganosilixane or silane coupling agents. Examples of
such surface treated silica powers are commercially available.
1 AEROSIL R972, R974, R202, R805, R812, RX200, RY200, R809, RX50,
RA200HS, RA200H (Nihon Aerosil Co.) WACKER HDK H2000, H2050EP, HDK
H3050Ep, HVK2150 (Wacker Cheminals, East Asia Nipsil SS-10, SS-15,
SS-20, SS-50, SS-6-, SS-100, SS-50B, SS-50F, SS-10F, SS-40, SS-70,
70, SS-72F (Nippon Silica Kogyo Co.) CABOSIL TG820F (Cabot
Speciality Chemicals Co.)
[0103] The content of the additive in the toner matrix is normally
0.05 to 5 weight %, and preferably 0.1 to 3 weight %.
[0104] It is possible to combine two types of silica powders, whose
average particle sizes differ from each other. The content of
silica powder relative to the toner matrix is normally 0.05 to 5
weight %, and preferably 0.1 to 3 weight %.
[0105] The toner produced as described above is used as a developer
for the electrophotography after being mixed with the carrier of
the present invention. Although there is no particular limitation
to the mixing ratio, 0.5 to 15 weight parts of toner is mixed with
100 weight parts of carrier.
[0106] The carriers for electrophotography of the present invention
and the electrostatic developing toner using the above carriers can
be used as the electrostatic developing agent in the two-component
developing machine, and this developing agent is particularly
favorable for use in the high speed developing machine which has a
developing belt speed of more than 20 m/min. and is further
favorable for a high speed machine of more than 30 m/min. The
present invention provides a developing agent or a developer, which
is capable of long printing for long time at a developing speed of
more than 45 m/min without causing photographic fogging or
inhomogeneous image quality.
EXAMPLES
[0107] The present invention will be explained in detail referring
to the Examples. Note that the present invention is not limited to
these Examples. In the following Examples and in Comparative
Examples, "%" represents "weight %", unless stated otherwise.
Example 1
[0108] (Preparation of Carrier)
[0109] 1 part of carbon black (Ketchen Black EC, trade name of a
product of Ketchen Black International Co.) and 10 parts of methyl
silicone resin (SR-2140, trade name of a product of Toray Dow
Silicone Co.) were dissolved in 100 parts of toluene and thus a
resin coating was formed. 200 g of ferrite core powder (average
particle size of 100 .mu.m) was prepared and the above resin
coating was coated on the ferrite core using a fluidized bed
(spiral flow) by controlling a ratio of coating resin to the core
powder at 2/10 (weight basis). After drying, the coated core powder
was heat treated at 250.degree. C. for 3 hours. 100 g of resin
coated ferrite powder was mixed with 250 g of zirconia beads 2 mm
in diameter and the mixture was then introduced into a resin bottle
with a volume of 500 ml. The bottle was rotated on a ball-mill
holder at a rotation speed of 100 rpm for 3 hours, and the carrier
A was obtained.
Comparative Example 1
[0110] The coated ferrite powder was prepared similarly to Example
1 until the coated ferrite powder was treated at 250.degree. C. for
3 hours. Then, the coated ferrite powder was stirred using zirconia
beads for 15 minutes and the carrier B was obtained.
Example 2
[0111] The coated ferrite powder was prepared similarly to Example
1 except controlling the ratio of the coating resin/core powder at
5/10 in the fluidized bed coating operation. Then, the coated
ferrite powder was processed similarly to the Example 1 and the
carrier C was obtained.
Comparative Example 2
[0112] The coated ferrite powder was prepared by the same process
as that of Example 1 until the coated ferrite powder was treated at
250.degree. C. for 3 hours. Then, the coated ferrite powder was
stirred using zirconia beads for 15 minutes and the carrier D was
obtained.
Example 3
[0113] The carrier D was obtained by the same procedure with
Example 1 except controlling the ratio of the coating resin/core
powder at 10/10.
Comparative Example 3
[0114] The coated ferrite powder was prepared similarly to Example
1 until the coated ferrite powder was treated at 250.degree. C. for
3 hours. Then, the coated ferrite powder was stirred using zirconia
beads for 15 minutes and the carrier E was obtained.
Example 4
[0115] After preparing the carrier similarly to Comparative Example
3, a dry etched processing was carried out using an ion sputtering
apparatus and the carrier G was obtained.
Resin Synthesis Example 1
[0116] The following materials and process yielded a polyester
rein.
[0117] 2.0 mol parts of terephthalic acid,
[0118] 2.5 mol parts of isophthalic acid,
[0119] 0.5 mol parts of trimellitic acid,
[0120] 4.0 mol parts of polyxyethylene(2,0)-2,
2-bis(4-hydroxyphenyl)propa- ne, and
[0121] 1.2 mol parts of ethylene glycol
[0122] were introduced into a four arm flask provided with a
stirrer, a condenser, and a thermometer, 0.07 weight parts dibutyl
tin oxide relative to all oxide components were added under a
nitrogen flow, all components were reacted at 220.degree. C. for 15
hours while removing water generated by the dehydration
condensation reaction, and a resin (A) was obtained. This polyester
resin (A) obtained by the above reaction showed the characteristic
temperature of 155.degree. C. at which the viscosity reaches
1.times.10.sup.5 poise and the acid value of 10.
[0123] The characteristic temperature at which the viscosity
reaches 1.times.10.sup.5 poise was measured by use of a constant
load extrusion capillary-type rheometer (Shimazu Flow Tester
CFT-500C, trade name of Shimazu Seisakusho Co.). The measurement
was performed under conditions such as a piston area of 1 cm.sup.2,
the cylinder pressure of 0.98 MPa, the die length of 1 mm, the die
hole diameter of 1 mm, measurement start temperature of 50.degree.
C., the temperature programming rate of 6.degree. C./min. and the
sample weight of 1.5 g.
Resin Synthesis Example 2
[0124] A resin was synthesized by using the following materials and
process.
[0125] 320 weight parts of styrene,
[0126] 60 weight parts of butylacrylate,
[0127] 20 weight parts of methacrylic acid
[0128] 4 weight parts of azobisisobutylolnitrile, and
[0129] 600 weight parts of xylene
[0130] were introduced into a round bottom flask, and after
reacting at 80.degree. C. for 10 hours under a nitrogen atmosphere,
the polymerization was completed by increasing the temperature to
130.degree. C. Thereafter, 2 weight parts of aluminum isopropoxide
was added and after reacting for approximately one hour, the
temperature was raised to 180.degree. C. and the pressure of the
flask was reduced to 0.5 mmHg for removing the solvent, and the
resin A was obtained.
[0131] This resin A obtained as described above has a
characteristic temperature at which the viscosity reaches
1.times.10.sup.5 poise of 145.degree. C., the glass transition
temperature Tg of 61.degree. C., and the acid value of 5.
[0132] Positive Charged Toner A
[0133] A toner product was obtained by the following procedure.
[0134] 92 weight parts of Resin A,
[0135] 5 weight parts of Morgan L carbon black (produced by Cabbot
Speciality Chemicals, Inc.),
[0136] 2 weight parts of refined carnauba wax No. 1 (acid value of
5, a product of CERA RICA NODA Co. Ltd.),
[0137] 1. 5 weight parts of charge control agent (BONTRON N-07
(Orient Chemical Co.),
[0138] 1 weight part of quaternary ammonium salt TP-302
[0139] were mixed using a Henschel mixer and were kneaded using a
biaxial kneader. The kneaded product was pulverized and sieved and
"Toner Product A" was obtained.
[0140] 100 weight parts of the above Toner Product A and
[0141] 1 weight part of Silica HDK3050EP (Wacker Chemicals Co.)
were mixed using a Henschel mixer and the mixture was passed
through a sieve. Finally, "Toner A" was obtained.
[0142] Positive Charged Toner B
[0143] 92 weight parts of Resin A obtained by Resin Synthesis
Example 1.
[0144] 5 weight parts of Morgan L carbon black (Cabbot Speciality
Chemicals Inc.),
[0145] 2 weight parts of polypropylene wax (550P, produced by Sanyo
Kasei Co.)
[0146] 1.5 weight parts of charge control agent (positive charge
control agent) "BONTRON N07 (Orient Chemicals Co.)
[0147] were mixed using a Henschel mixer and kneaded using a
biaxial kneader. The kneaded product was pulverized and sieved and
"Toner product B" was obtained having an average particle size of
10.2.
[0148] "Toner B" was obtained by mixing 100 weight parts of the
above "Toner Product B" with 1 weight part of Silica HDK3050EP
(Wacker Chemicals Co.) and the mixture was thereafter passed
through a sieve.
[0149] Evaluation 1 (Measurement of Carbon Content and Slope)
[0150] Values "A" for Examples 1, 2 and 3 and Comparative Examples
1, 2 and 3. Furthermore, using the AC-1, values B were also
obtained. The results were shown in Table 1.
2 TABLE 1 right side of (A) (weight %) (B) the equation Example 1
Carrier A 0.15 33.4 28.1 Comparative Carrier B 0.16 24.7 27.9
Example 1 Example 2 Carrier C 0.31 28.2 25.0 Comparative Carrier D
0.33 22.4 24.6 Example 2 Example 3 Carrier E 0.47 29.3 21.9
Comparative Carrier F 0.49 16.2 21.5 Example 3 Example 4 Carrier G
0.49 25.3 21.5
[0151] As shown above, Examples 1, 2, 3, and 4 satisfy the equation
defined by the present invention. However, Comparative Examples 1,
2, and 3 do not satisfy the equation.
[0152] Evaluation 2 (Measurement of Charge Build-Up)
[0153] (Adjustment of Developer)
[0154] "Developer (A/A)" was adjusted by mixing 6 weight parts of
the above-described "Toner A" with 114 weight parts of carrier A in
a cylinder-type polyethylene container having a diameter of 5 cm
and a length of 6 cm.
[0155] Similarly, a series of developers shown in Table 2 were
obtained.
3TABLE 2 Developer (A/B) 6 wt. parts of Toner A 114 wt. parts of
Carrier B Developer (A/C) 6 wt. parts of Toner A 114 wt. parts of
Carrier C Developer (A/D) 6 wt. parts of Toner A 114 wt. parts of
Carrier D Developer (A/E) 6 wt. parts of Toner A 114 wt parts of
Carrier E Developer (A/F) 6 wt. parts of Toner A 114 wt parts of
Carrier F Developer (A/G) 6 wt. parts of Toner A 114 wt parts of
Carrier G Developer (B/A) 6 wt. parts of Toner B 114 wt parts of
Carrier A Developer (B/B) 6 wt. parts of Toner B 114 wt parts of
Carrier B Developer (B/C) 6 wt. parts of Toner B 114 wt parts of
Carrier C Developer (B/D) 6 wt. parts of Toner B 114 wt parts of
Carrier D Developer (B/E) 6 wt. parts of Toner B 114 wt parts of
Carrier B Developer (B/F) 6 wt. parts of Toner B 114 wt parts of
Carrier F Developer (B/G) 6 wt. parts of Toner B 114 wt parts of
Carrier G
[0156] The polyethylene container containing each developer was
stirred for 3 minutes at a rotating speed of 115 rpm, and then the
amount of electro-static charge was measured using an electrostatic
charge meter (Blow-Off Electrostatic Charge Meter: Toshiba
Chemicals Co.). Furthermore, stirring was performed for 7 minutes
(10 minutes in total) and the amount of electrostatic charge was
measured similarly. The results were shown in Table 3.
4 TABLE 3 amount of charge (.mu.C/g) after 3 min. after 10 min.
Developer (A/A) 7.5 7.9 Developer (A/B) 2.9 4.0 Developer (A/C) 6.7
7.2 Developer (A/D) 1.2 3.1 Developer (A/E) 5.6 6.0 Developer (A/F)
-0.7 0.2 Developer (A/G) 4.7 5.1 Developer (B/A) 8.3 7.6 Developer
(B/B) 5.8 7.5 Developer (B/C) 8.3 7.7 Developer (B/D) 5.3 7.1
Developer (B/E) 8.1 7.9 Developer (B/F) 4.9 7.0 Developer (B/G) 7.4
7.2
[0157] As seen in the above Table 3, the electrostatic charge rose
rapidly in those developers containing respective carriers A, C, E,
and G, and the amount of charge stored in those developers
containing respective carriers A, C, E, and G were stably
maintained. In contrast, the charge did not rise rapidly in
developers containing respective carriers B, D, and F, and, in
particular, the developer (A/F) was charged negatively.
[0158] Evaluation 3 (evaluation of print)
[0159] Test printings were conducted in a commercial printing
machine (XC-8 10 a product of Fuji Xerox Corporation) using the
developers after being stirred for 10 minutes in the previous
Evaluation 2.
5 TABLE 4 Chemical fogging Developer (A/A) OK Developer (A/B)
unsatisfactory Developer (A/C) OK Developer (A/D) unsatisfactory
Developer (A/E) OK Developer (A/F) OK Developer (A/G)
unsatisfactory Developer (B/A) OK Developer (B/B) unsatisfactory
Developer (B/C) OK Developer (B/D) unsatisfactory Developer (B/E)
OK Developer (B/F) unsatisfactory Developer (B/G) OK
[0160] As seen in Table 4, clean images are obtained having no
fogging were obtained when the carriers A, C, E, G were used.
However, foggy images were obtained when carriers B, D, and F were
used.
[0161] When the carriers for electrophotography of the present
invention are used as developers after mixing with toners, these
carriers in the developers not only charge the toner very rapidly
to a target charge amount, but also maintain the target amount of
charge during printing, so that the chemical fogging and the image
density, respectively related to the initial charging and the
charge maintenance properties, can be eliminated.
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